Reactors which are inductance parts including a core having a built-in coil configured of a wound electric wire have conventionally been used in various fields.
For example, in hybrid vehicles, fuel cell vehicles, electric vehicles, or the like, a booster circuit has been disposed between the battery and the inverter which supplies alternating current power to a motor (electric motor), and a reactor (choke coil) which is an inductance part is used in the booster circuit.
In hybrid vehicles, for example, the battery has a voltage of about 300 V at the most, while it is necessary to apply a high voltage of about 600 V to the motor so as to obtain high output. A reactor is used as a part for the booster circuit for that purpose.
Such reactors are in extensive use in booster circuits for photovoltaic power generation and in other applications.
Conventionally known as such a reactor is an injection-molded reactor produced by injection-molding a mixture of a soft magnetic powder and a resin binder including a thermoplastic resin to thereby configure a core so that a coil obtained by winding a electric wire is embedded therein without leaving any space therein.
This kind of injection-molded reactor is disclosed, for example, in the following patent document 1.
In the injection-molded reactor, polyphenylene sulfide (PPS) resins, polyamide (PA) resins, polyetheretherketone (PEEK) resins, and the like, which have a melting point of 150° C. or higher and are excellent in terms of high heat resistance, flame retardancy, mechanical strength, and the like may be suitably used as the thermoplastic resin forming the resin binder of the core.
In this case, any of these resins including PPS resins, PA resins, and PEEK resins is usually used alone to constitute the whole thermoplastic resin.
Incidentally, in the case where an alternating magnetic field is applied to an injection-molded reactor to operate the reactor, the hysteresis loss and eddy current loss caused in the core result in a loss (core loss) whereby the applied energy is partly released in the form of heat. In injection-molded reactors in which the whole thermoplastic resin forming the resin binder of the core is constituted only of a resin excellent in terms of high heat resistance, flame retardancy, mechanical strength, etc., such as a PPS, PA, or PEEK resin, there has been a problem in that the loss is not sufficiently small.
The following patent document 2 discloses an invention which relates to “an injection-molded soft magnetic body and a soft magnetic kneaded mixture” as a prior-art technique relevant to the present invention, and polyphenylene sulfide resins, polyamide resins, polyester resins, polyethylene resins, polypropylene resins, epoxy resins, and the like are shown therein as examples of the resin used in the injection-molded soft magnetic body.
However, patent document 2 discloses neither the feature of using a combination of resins differing in melting point nor the feature of controlling the addition amount of a resin having a low melting point.